Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 367

Brazil, and both found that where rotations with N 2 -ixing legumes were included,
much more SOM was accumulated, hence highlighting the fact that for there to be an
accumulation of SOM, there must be not only a C input from crop residues but also
a net input of N. They further postulated that where net N balance was close to zero
over the whole crop rotation, little SOM accumulation was to be expected. Amado
et al. (2006) reported that pigeon pea and Mucuna cover crops integrated into
no-till maize cropping systems had the highest C accumulation rates under no-till
than that of the intensive cropping systems, including mixtures of black oat with
hairy vetch in winter and maize with cowpea in summer. Sá et al. (2001a) suggests
that the immobilization process is most intense during the first years of no-till but,
after 5 or more years, gradually diminishes due to the increased surface concentra-
tion of SOM acting as an N source, thereby effectively counteracting N limitations
induced by residues input on the soil surface.
Both in tropical and subtropical Brazil, legume residues left on the soil surface
decompose rapidly and provide a prompt N release, sometimes so fast that it causes
asynchronies with maize demand (Acosta 2005; Aita and Giacomini 2003; Vinther
2004). Common vetch residue left on the soil surface in Santa Maria, for example,
released 60 kg of N per hectare in only 15 days (Acosta 2005).
14.5.3.2 Australia
Australian farmers became increasingly concerned about soil degradation during
a dry period in the 1970s. They saw how plowing of the soil was not sustainable
in such an unforgiving and harsh climate (Crabtree 2010). There were also other
dry periods where soil erosion was a serious concern, particularly in the 1930s and
then potentially again in the first decade of the 2000s. However, during this recent
decade, Australian farmers were prepared! They had widely adopted no-till farming,
and this greatly mitigated the severely damaging effects on the soil and maintained
financial viability during such droughts.
No-till solved most degradation: An in-depth Australian experience with land
degradation and the usefulness of no-tillage techniques to manage these concerns
are well documented in Crabtree (2010). It was wind erosion concerns that initiated
farmers' determination to find a better way to farm. There was no other soil degrada-
tion concern that motivated farming practice change. As two broad-spectrum herbi-
cides, SpraySeed (paraquat:diquat) and Roundup (glyphosate), became available in
the early 1980s, farmers began reducing their reliance on tillage. Through trial and
error, both farmers and researchers gained confidence in the technique (Crabtree
1983, 2010; Flower et al. 2008).
While the initial adoption was slow, the technique of spraying herbicides, and
then planting the crop, with little soil disturbance, was the beginning of no-tillage
in Western Australia. The experience of farmers revealed many other soil benefits.
In fact, most of the concerns with soil degradation were significantly mitigated with
no-tillage through time.
No-till both improved soil structure with less vehicle compaction and increased
the steady state of microbial activity, which gave the soils some biological struc-
ture. Waterlogging became less common due to better infiltration (and some dryer
years). Soil salinity was somewhat mitigated as soil water runoff was less common